The invention relates to a ring of cells for analytical devices operating on the centrifugal principle and photometrically measuring a sample for analysis, the system comprising a number of individual cells disposed in a circle and made of thermoplastics, each cell having three interconnected chambers, i.e. a sample chamber, a reagent chamber and a photometric measuring chamber, the major axes of the sample chamber and the reagent chamber being at right angles to the plane of rotation and the major axis of the measuring chamber coinciding with the plane of rotation.
Some known analytical devices operate on the centrifugal principle and make photometric measurements of the sample for analysis. They are preferably used when very small samples have to be analysed in a short time and where the nature of the analysis is such that photometric methods can be used. This applies particularly to clinical chemical analysis, where it is frequently necessary e.g. to determine glucose, urea, uric acid, cholesterol or total protein, albumin, bilirubin or metal ions in the blood, serum, plasma, urine or liquid obtained by puncture, e.g. liquor or similar biological solutions. The amount of material available for investigation is frequently only a few microliters and the time available for analysis is often limited to a few minutes. In such cases it is advantageous to use automatic analytical devices operating by the aforementioned centrifugal method.
The devices comprise a ring of cells containing a predetermined number of individual cells. Each individual cell has at least three chambers, i.e. a sample chamber, a reagent chamber and a photometric measuring chamber. The sample and the reagent are poured into the appropriate cell chambers when the rotor is motionless, so that the two liquids initially remain separate. After the cells have been filled, the analyzer is started up, whereupon the centrifuge first rotates at high speed. As a result of centrifugal force, the sample for analysis and the reagent liquid are expelled from the two chambers into which they were previously poured, and are combined and raised to the photometric measuring chamber. After a predetermined time, the photometric scanning of the individual measuring chamber begins, and usually the peripheral speed of the centrifugal part of the analyzer is reduced. The extinction recorded by the measuring part is evaluated by a computer and is usually immediately expressed as the result of the analysis.
Known centrifugal analyzers of this kind, e.g. as described in the "Cobas-Bio" pamphlet published in 1978 by Messrs. F. Hoffmann-Laroche & Co. of Basle, comprise a number of individual cells combined to form the aforementioned ring of cells by means of a separate ring. The ring has a number of radial slots in which the cells with their oblong measuring chambers are inserted and retained. The advantage of the device is that individual cells can be thrown away after use and destroyed if necessary, which is particularly important in the analysis of pathogenic liquids.
German Offenlegungsschrift No. 27 26 219 corresponding to U.S. Pat. No. 4,123,173 discloses a cell system for centrifugal analyzers having a different construction. According to the last citation, the cell system comprises two superposed discs of flexible thermoplastics, the lower disc being formed with a number of compartments and the top disc being stuck or welded to the bottom disc and, in the process, covering at least part of each compartment. Cell systems of this kind form an inseparable unit which, as before, has good mechanical stability but where it is impossible to remove individual cells from the unit and destroy them separately.